Ask Dr. Math
High School Archive
Dr. Math Home ||
Middle School ||
High School ||
Dr. Math FAQ
See also the
Browse High School Logarithms
Stars indicate particularly interesting answers or
good places to begin browsing
- No Logarithm of a Negative Number [8/6/1996]
log(-5) = ?
- Origin of the Term Logarithm [10/27/1999]
Where does the term logarithm come from?
- Perfect Logarithms [06/24/2002]
What can you tell me about the equation log(abc)= log(a+b+c)?
- Population Growth Rate [9/5/1996]
If a population increases from 10 million to 300 million in 10,000 years,
what is the annual growth rate?
- Population of China [05/13/1997]
If the population growth rate of China is 4.3 percent and the current
population of the country is 1.27 billion people, when will the
population reach 2 billion?
- Proof by Contradiction [05/09/2003]
Show that the log_2(7)/log_2(6) is irrational.
- Radioactive Decay [10/26/2004]
The half-life of a radioactive element is 131 days, but your sample
will not be useful to you after 90% of the radioactive nuclei
originally present have disintegrated. For about how many days can you
use the sample?
- Repeated Square Roots and Logarithms [04/05/2005]
A discussion based on a calculator trick where taking 'n' repeated
square roots of 'a', then subtracting 1 and multiplying by 'b', then
adding 1 and squaring 'n' times, leads to a result very close to a^b.
The explanation is closely related to logarithms.
- Resolving Decimal Exponents [03/26/2001]
How can you find 7^.3 or 5^.6 without using a calculator? Is there more
than one way of doing this?
- Richter magnitude problem [11/23/1994]
The Richter magnitude, R, of an earthquake is given by R=0.67
log(0.37E)+1.46 where E is the energy in kW*h released by the earthquake.
Show that if R increases by 1 unit, E increases by a factor of about 31.
- Roughing It More Rigorously [12/02/2010]
A physics student wants to make sense of the various symbols used to represent "approximately equal to" -- as well as the phrase's mathematical meaning. Doctor Vogler produces two precise definitions while acknowledging that context, and personal preference, rule the day.
- Seventy-two and 115: What Do Logs Have to Do with Doubling and Tripling Your Money? [02/19/2010]
Doctor Carter uses logarithms and the Taylor series to show where the
72 in the "law of 72" comes from -- and shows how the same interest
rate calculations yield 115/I as an approximation for the number of
years it takes an investment that bears I interest rate to triple in
- Slide Rules [03/13/1999]
Can you help me learn how to use a slide rule?
- Solving a Decibel Noise Equation [05/23/2000]
How do you rearrange the formula 50 = 94.5 - 20log(r) - 8 to solve for r?
- Solving a Logarithm Equation by Substitution [12/18/2007]
I'm learning about logs, and had to solve (x+1)^(log(x+1)) = 100(x+1).
My answers don't check. Can you show me where I went wrong?
- Solving Logarithm Equations [04/29/2001]
How can I solve the equation: log_7(x) / log_7(4) - log_7(y) = 1, for y?
- Solving Logarithms with the Quotient Rule [11/11/1998]
Can you help me solve this logarithm problem for x? I think you need to
use the quotient law.
- Solving Log Equation [04/20/2008]
Given log(x) + log(x + log(x)) + log(x + log(x) + log[x + log(x)]) =
0, how can I solve for x?
- Solving Logistic Equations for a Variable in the Exponent [05/03/1998]
Using natural logarithms to solve for the time variable in two logisitic
- The Symbol for Natural Log [06/28/2000]
Why is "ln" and not "nl" the abbreviation for natural log?
- Taking the Logarithm of Zero [08/11/2004]
Why is log(0) undefined?
- Uses of Logarithms [07/20/2002]
Who uses logarithms, and for what?
- Using a Rule of Logarithms [9/13/1995]
I can't figure out this problem. Can you help? log(sub)2 3k+log(sub)2
- Using Logarithms to Find Number of Digits in Large Numbers [06/25/2007]
How many digits are there in 8^1000? What power of 8 has 1000 digits?
What number to the 1000th power has 500 digits?
- What Does x Equal? [01/16/1998]
32 * 4^2x = 12. What is x? What is a logarithm?
- Why Do We Learn Logarithms? [02/28/2005]
I am currently studying logarithms in school and I was wondering what
the point of them is. Will we ever use them when we grow up, and how
are they used in real life?
- Why Use a Logarithmic Scale to Display Data? [01/26/2008]
I read that log scales help you see data when you are looking at
values that range largely. I also read that if the ear did not hear
logarithmically we would only hear very loud sounds. Can you help me
understand these two statements?
Search the Dr. Math Library:
© 1994-2015 Drexel University. All rights reserved.
Home || The Math Library || Quick Reference || Search || Help
The Math Forum is a research and educational enterprise of the Drexel University School of Education.